1. Field of the Invention
The present invention relates to a D.C. flat motor, and specifically relates to improvement of the inside structure of the flat motor in order to make the assembly of the motor easy and increase the productivity of the motor.
2. Description of the Prior Art
The conventional D.C. flat motor is constructed, for example, as shown in FIG. 12. Flat motor 1 has upper and lower motor housings 2 and 3, a resin holder plate 4 attached onto the lower housing 3 coaxially with the lower housing, and a ring-like shaped magnet 5. A pair of brush holders 6 are provided on holder plate 4 and a brush 7 is inserted into each of the brush holders. Brush 7 is urged by an urging device such as a spring (not shown) so as to come into contact with commutator 9 of armature 8.
In such a type of flat motor, motor housing 3, holder plate 4 and magnet 5 are required to be arranged coaxially with one another. However, means for disposing these members coaxially is not provided in the conventional flat motor itself. Therefore, in assembly of the conventional flat motor, a jig is used for disposing these members coaxially, particularly for disposing magnet 5 coaxially with motor housing 3, the centers of both members are met by the jig when the magnet is bonded to the motor housing by an adhesive, and then, the magnet is fixed to the motor housing by the jig until the adhesive is cured.
In such a method for assembly of a flat motor, however, since the number of jigs must correspond to the production number of the motors which are produced during the curing time of the adhesive, a large number of jigs are required and the cost of the jigs is relatively high. Moreover, since jigs must be used for assembly, the work to be done during assembly is troublesome.
In the assembly of the above flat motor 1, there is one method wherein resin holder plate 4 is fixed directly to motor housing 3 by an adhesive and another method wherein the holder plate is fixed to the motor housing via screws or rivets 10. FIGS. 13 and 14 show the latter case.
In the case where holder plate 4 is bonded to motor housing 3 by only an adhesive, however, since the bonding strength between the resin of the holder plate and the metal of the motor housing is only about 1/4 of the bonding strength between metals, the bonding strength is often insufficient, thereby decreasing the reliability and durability of the motor.
In the case where the holder plate 4 is fixed to the motor housing 3 via screws or rivets 10, through holes 11 must be formed in the motor housing for inserting the screws or rivets, as shown in FIGS. 13 and 14. In such a structure, there is a fear that water may seep into the motor through the holes 11 and cause the inside of the motor to rust. Moreover, since the process of inserting and fastening the screws or rivets is necessary, the work during assembly becomes troublesome and the cost for the production of the motor becomes large.
After assembling holder plate 4 and magnet 5 coaxially with motor housing 3, armature 8 including commutator 9 is inserted. During this insertion, since each brush 7 is urged inward by the urging device, the motion of the brush is stopped by a tweezers-like shaped jig and the brush is held in brush holder 6 against the urging force of the urging device. Then, commutator 9 is inserted between a pair of brushes 7 down to a position where the magnetic gap between armature 8 and magnet 5 is set to a predetermined small gap.
In order to insert commutator 9 down to a position where the magnetic gap reaches a predetermined small gap, however, the jig for the insertion must be small and flexible. The conventional tweezers-like shaped jig cannot sufficiently satisfy such a requirement.